Isotopic scaling features of molecular ions and their descendants

Pablo Serra, Sabre Kais, Juan Pablo Neirotti

Sabre Kais, Juan Pablo Neirotti, Pablo Serra

Onoda Shinobu, Kimura Kosuke, Oguro Tsubasa +5 more

A nitrogen vacancy (NV) center in diamond is known as a solid-state spin quantum bit (qubit) at room temperature. The fabrication of scalable quantum registers based on NV centers is a long-standing issue. In 2005, spin-spin interaction between NV-N pairs, which were fabricated by N2 ion implantation, was reported. An entanglement between two electron-spin qubits becomes an excellent quantum information processing component, as accomplished by an NV-NV pair with a nanometer-scale distance in 2010 and 2013. More recently,strongly dipolar coupled NV-NV pairs were realized by 14N 30 keV implantationvia nanoholes in PMMA resist mask. The creation yields of NV-NV pairs dramatically improved, and the nanohole implantation had been thought to be the most promising technique to integrate NV centers. However, the problem of the technique is the finite size of nanoholes. The distribution of nitrogen atoms is determined by both ion straggling and nanohole diameter. The scaling of NV centers is stagnant up to two for several years. To overcome the barrier of triple NV centers, our previous research gave a ground-breaking idea of a highly populated NV center complex by introducing a molecular ion implantation technique in 2019. Since the molecular ion is regarded as an idea point source, the distribution of nitrogen atoms is determined by only ion straggling. Therefore, our proposed method is more effective than other implantation techniques including nanohole implantation. Instead of a pure nitrogen cluster which is commonly unstable, the stable organic molecular ions (adenine; C5N5H5) were utilized as the ion source. We successfully implanted C5N4Hn ions into single crystalline diamonds. Three NV centers were integrated, and the dipolar interactions among them were successfully observed. In 2022, we succeeded in creating more than 5 NV centers by phthalocyanine (C32H18N8) ion implantation. The next challenge is the implantation of isotopically enriched molecular ions. The isotopically enriched ion contains 13C and 15N. The implantation of isotopically enriched molecular ions is able to create 15NV-13C hybrid quantum registers. In this presentation, we will show the development of the isotopically enriched molecular ion beam and the characterization of created NV centers by laboratory-built confocal microscopy (CFM) and optically detected magnetic resonance (ODMR).

Mason Adshead, Maddison Coke, Evan Tillotson +12 more

ABSTRACT A reliable route to the deterministic fabrication of impurity ion donors in silicon is required to advance quantum computing architectures based upon such systems. This paper reports the ability to dope isotopically‐defined unique ( 121 Sb 123 Sb) 2+ molecular ions into silicon with measured detection efficiencies of 94% being obtained. Atomically resolved imaging of the doped Sb ions reveals substitutionally incorporated atoms with a Sb‐to‐Sb separation of ≈2 nm post‐implantation, thus indicating suitability to form coupled qudit systems. Molecular dynamics simulations support the preference for doped Sb atoms to occupy lattice sites, driven by fast (≈1s) re‐crystallization of localized ion implantation induced damage at 300 K. The Sb doping method used is fully compatible with integration into processing that includes pre‐enrichment of the silicon host to sub‐3 ppm 29 Si levels. As such, we present a potential pathway to the creation of scaled qudit arrays within silicon platforms for quantum computing.

Maxim Sirotin

Atomic parity violation (APV) provides a low-energy probe of the weak interaction between electrons and nuclei, complementary to collider tests of the Standard Model. Isotope-chain measurements are especially attractive because they test weak-charge scaling while reducing dependence on absolute atomic-structure theory. We review the APV mechanism, the state of the art in Cs and Yb, and recent trapped-ion, optical-lattice, and molecular proposals. Motivated by progress in coherent control of atoms, ions, and molecules, we ask a metrological question: given N probes distributed over an isotope chain, what quantum strategy optimally measures a deviation from Standard Model weak-charge scaling? The optimum is a particular form of a cross-isotope cat state protocol. We compare this protocol with the standard quantum limit, squeezed-array, same-isotope cat, and discuss extension to recently suggested decoherence-free subspace protocols. We show that entanglement can strongly accelerate statistical averaging, but the ultimate precision is set by APV-specific systematic floors which require careful studies.

Werner Neuhauser, M. Hohenstatt, P. E. Toschek +1 more